The present invention relates generally to electrical interconnects. The present invention relates more particularly to a microelectronic contact assembly having a plurality of metallic springs and an elastomeric pad which cooperate to effect reliable electrical contact between raised interconnection features, such as bump contacts, formed upon a flexible circuit and contact pads of an electronic device.
It is frequently desirable to attach electronic devices, such as integrated circuits or printed circuit boards, to flexible circuits. Flexible circuits typically have bump contacts or the like formed thereon to facilitate such attachment. The bump contacts of the flexible circuit provide electrical contact to corresponding contact pads of the electronic device so as to facilitate electrical communication between the flexible circuit and the electronic device.
According to contemporary practice, compressive force is applied to the flexible circuit so as to urge the bump contacts thereof into intimate contact with the corresponding contact pads of the electronic device. This compressive force is typically applied via a clamp and/or fastener arrangement which defines an attachment device or connector for maintaining the desired mechanical contact of the bump contacts of the flexible circuit with the contact pads of an electronic device. Occasionally, an elastomeric pad is provided on the opposite side of the flexible circuit, with respect to the bump contacts, in an attempt to maintain adequate compressive force over time. Thus, the elastomeric pad is compressed substantially by the clamping device and/or the fasteners which hold the flexible circuit in position with respect to the electronic device.
In this manner, the elastomeric pad is captured within the attachment device and is compressed as the bump contacts of the flexible circuit are urged into intimate contact with the corresponding contact pads of the electronic device. The compressed elastomeric pad generally continues to apply a compressive force to the bump contacts of the flexible circuit in an attempt to maintain the intimate contact of the bump contacts with the contact pads for a prolonged period of time.
As those skilled in the art will appreciate, such elastomeric pads additionally provide compliance by allowing the bump contacts of the flexible circuit to move with respect to the plane within which they are nominally formed. That is, the bump contacts are permitted to move generally at right angles with respect to this plane, so as to compensate for non-coplanar alignment of the corresponding contact pads of the electronic device. In this manner, the elastomeric pad tends to assure reliable contact of the bump contacts of the flexible circuit with the contact pads of the electronic device, even though there may be imperfections in the planar alignment of the contact pads of the electronic device.
Further, such elastomeric pads tend to concentrate the compressive force generally at the locations of the bump contacts, where the compressive force is needed. Since the compressive force tends to be concentrated in such a manner, the total clamping force may be reduced, thus facilitating construction of the attachment device of lighter and less expensive materials. Thus, the use of a resilient pad assures that the compressive force is selectively concentrated upon the contact feature, instead of being distributed across the entire terminus array.
However, as those skilled in the art will appreciate, such elastomeric pads tend to take on a mechanical compression set when compressed for a prolonged period of time, whereby such elastomeric pads tend to lose at least a portion of their resiliency. Thus, the compressive force applied by such elastomeric pads tends to degrade or lessen over time. This effect is particularly pronounced when elastomeric pads are subjected to harsh environments, such as elevated temperatures.
Frequently, modern high-density interconnects are used to communicate signals at comparatively high frequencies. The operation of interconnects at such high frequencies may result in heat build up, which is detrimental to the lasting effectiveness of elastomeric pads. Additionally, such interconnects are frequently used in automotive and other electronic applications, wherein the temperature of the environment is inherently elevated. For example, such interconnects may find applications in facilitating electrical communication between engine transducers and the dashboard of an automobile. In such applications, it is generally desirable that the electronic devices for which communication is facilitated by the interconnect operate reliably.
In view of the foregoing, it is desirable to provide an electronic interconnect having a compliant structure for facilitating reliable electrical contact of the bump contacts of a flexible circuit with the contact pads of an electronic device, wherein the electronic interconnect is not substantially susceptible to mechanical compression set.
The present invention specifically addresses and alleviates the above-mentioned deficiencies associated with the prior art. More particularly, the present invention comprises an electronic interconnect which includes a flexible circuit having a plurality of contacts formed thereon, a plurality of springs positioned so as to apply a compressive force to at least one of the contacts when the electronic interconnect is mated, and a resilient material configured to apply a compressive force to at least one of the springs.
According to the preferred embodiment of the present invention, the contacts formed upon the flexible circuit comprise bump contacts. The bump contacts are preferably formed upon the flexible circuit so as to define an array of bump contacts. The array of bump contacts may be of any desired shape. For example, the array of bump contacts may be generally circular, triangular, square, rectangular, hexagonal, octagonal, etc.
The springs preferably comprise metallic springs. The metallic springs are preferably formed so as to define an array thereof. The array of metallic springs will generally conform in shape to the array of bump contacts. Thus, for example, if the array of bump contacts is square, then the array of springs will typically be square as well. Generally, each pad possessing bump contacts (some pads have more than one bump formed thereon) has a dedicated metallic spring, so that there is a one-to-one correspondence between pads and metallic springs.
It is important to understand that each pad may optionally comprise more than one bump contact. For example, a single pad may have two, three, four or more separate bump contacts formed thereon. The use of a plurality of bump contacts for a single pad is generally done so as to enhance the reliability of the connection formed thereby. As those skilled in the art will appreciate, the use of such a plurality of bump contacts substantially enhances the reliability of electrical contact by providing a plurality of surfaces through which contact is made.
Thus, according to the preferred embodiment of the present invention, the contacts comprise an array of bump contacts and the springs comprise a corresponding array of springs, wherein each spring is configured so as to apply a compressive force to a dedicated pad possessing bump contacts when the interconnect is mated. The springs are disposed on an opposite side of the flexible circuit with respect to the contacts.
The resilient material preferably comprises a sheet of elastomer, e.g., an elastomeric pad, which is configured so as to apply compressive force to the springs when the interconnect is mated. The elastomeric pad applies a compressive force which is substantially localized to each individual bump contact. However, the use of an elastomeric pad alone would be subject to the problems associated with the elastomeric pad eventually taking a mechanical compression set, thereby losing at least some portion of the compressive force applied thereby. According to the present invention, the array of metallic springs continues to provide a compressive force to the bump contacts, even in the event of the elastomeric pad undergoes a mechanical compression set.
Preferably, the elastomeric pad is configured to facilitate substantially independent movement of the metallic springs with respect to one another, so as to provide the desired compliance. That is, the combination of the elastomeric pad and the array of metallic springs is flexible or bendable, such that the elastomeric pad and the metallic springs can move so as to accommodate imperfections in the planarity of the contact pads of the electronic device.
Thus, according to the present invention, each spring is configured so as to apply compressive force to only a dedicated pad possessing bump contacts when the electronic interconnect is mated. The elastomeric pad is preferably configured so as to facilitate substantially independent movement of the metallic springs with respect to one another, wherein such independent movement is generally orthogonal to the plane of the springs. Such orthogonal movement of the springs thus provides compliance which facilitates a reliable interconnection of a plurality of closely spaced bump contacts of a flexible circuit with corresponding contact pads of an electronic device, particularly when the contact pads of the electronic device are not substantially coplanar with respect to one another.
The combination of the elastomeric pad and the metallic springs tends to concentrate compressive force generally at the locations of the bump contacts, such that less overall compressive force is required to effect reliable contact between the bump contacts of the flexible circuit and the contact pads of the electronic device. Because less overall compressive force is required, the clamping structure of the connecting device (which effects mechanical attachment of the flexible circuit to the electronic device) can be made of less expensive materials. As those skilled in the art will appreciate, contemporary clamping structures are generally constructed of metal, such that they are capable of applying the necessary, comparatively high, compressive force required to effect reliable connection of the bump contacts of flexible circuits to the contact pads of an electronic device.
These, as well as other, advantages of the present invention will be more apparent from the following description and drawings. It is understood that changes in the specific structure shown and described may be made within the scope of the claims without departing from the spirit of the invention.